Success in treatment of anthrax is critically dependent on rapid diagnosis. As a consequence, there is an acute need for diagnostic tools that can be used in a first responder clinical setting where anthrax will be initially encountered. Detection of microbial antigens in body fluids is a proven technology in diagnosis of infectious disease. Bacillus anthracis is surrounded by an anti-phagocytic capsule that is composed of poly-y-D-glutamic acid (PGA), raising the possibility than immunoassay for PGA could be a means for early, specific, rapid and inexpensive diagnosis of anthrax. To date, development of an immunoassay for PGA has been hampered by the poor immunogenicity of PGA and the complete absence of information regarding production of PGA in vivo. In preliminary experiments, high affinity monoclonal antibodies (mAbs) reactive with PGA were produced and used to construct an immunoassay for PGA. The assay has an extraordinarily high sensitivity, with a lower limit near 100 pg/ml. The immunoassay was used to assess PGA antigenemia in a murine model of inhalation anthrax. The results showed that the initial presence of detectable PGA in blood coincided with the occurrence of detectable bacteremia. Full bacteremia was accompanied by a massive antigenemia with antigen titers as high as 1/5,000,000 48 h after infection. Six specific aims are proposed: i) to identify the immunochemical variables that influence the performance of immunoassay for PGA, ii) to evaluate the efficacy of an immunoassay for diagnosis and assessment of prognosis and treatment in a murine model of inhalation anthrax, iii) to assess tissue distribution and pharmacokinetics for clearance of PGA in vivo, iv) to develop, in cooperation with a private sector partner, a prototype "potential ultimate product" for antigen detection in anthrax, v) to determine the specificity of a PGA-based immunoassay for anthrax, and iv) to evaluate the efficacy of PGA immunoassay a non-human primate model of anthrax. This is a translational study that has the potential to dramatically impact diagnosis and treatment of anthrax. The study takes advantage of a library of PGA mAbs that is already in hand and optimizes a proven technology for use with PGA, a heretofore understudied class of microbial antigens. The overall goal is production of a prototype immunoassay for PGA that can be used in a first responder clinical setting where anthrax will be initially encountered.